Fourth-quarter results dented lofty hopes that a new age of profitability is at hand

Amazon.com reported its highest quarterly profit ever. Wall Street made the mistake of expecting even more.

The e-commerce giant reported fourth-quarter sales and earnings late Thursday that fell short of analyst expectations. Investors haven’t historically given much thought to profits at Amazon. They have instead focused on top-line growth with the expectation the company’s heavy investment would pay off at some undetermined point...